1. Field of The Invention
This invention relates to sprue bushings. More particularly, it refers to sprue bushings having a water jacket for controlling the melt viscosity of molten plastic moving through the bushing.
2. Description of The Prior Art
Sprue bushings are commonly used in the injection molding of plastic materials to convey the molten plastic from the injection molding machine to the cavities of the mold. Different apparatus and methods have been employed in the prior art to control the melt viscosity of the molten plastic to insure an adequate supply to the cavities without undue extending sprue. U.S. Pat. No. 4,260,348 describes a sprue bushing having longitudinal grooves to form channels for inlet and outlet water to control the temperature of the molten plastic at about 170.degree. F. U.S. Pat. No. 4,004,871 describes an apparatus having a water supply conduit to a mold gate insert assembly to maintain the particular plastic material employed at the proper setting temperature.
Although these prior art apparatus and methods control melt viscosity to some degree, a sprue bushing is needed that can be easily installed and employed to control melt viscosity of a wide variety of different plastics